1. Field of the Invention
This invention relates in general to spin coating machines that are used to coat a layer of liquefied material, such as spin-on-glass (SOG) or photoresist, with high degree of planarization on a semiconductor wafer. More particularly, this invention relates to a detachable sponge device for a spin coating machine, which is capable of preventing the solvent that is jetted on the edge of the wafer for edge bead rinse (EBR) purpose from being oversprayed elsewhere on the wafer.
2. Description of Related Art
As integrated circuits are fabricated to contain more and more components therein for increased scale of integration, a single wafer is usually divided into multiple layers so that it can contain a vast amount of components therein. This kind of wafer needs to use highly planarized dielectric layers to separate between the multiple layers thereof. One method to form the highly planarized dielectric layers is to use the so-called spin-on-glass (SOG) process to coat a liquefied dielectric material, such as silicon dioxide, on the wafer. The SOG process is usually conducted by a so-called spin coating machine which spins the wafer while the liquefied silicon dioxide is being applied onto the wafer. As a result, due to the centrifugal force from the spinning, the liquefied silicon dioxide can be spread evenly over the wafer so that the planarization of the coating of silicon dioxide is highly effective.
FIG. 1 shows a schematic sectional diagram of a conventional spin coating machine, which has a bowl-shaped area inside 10 including a vacuum chuck 11 therein for securely holding a semiconductor wafer 12 thereon. The vacuum chuck 11 is driven by a servo motor 13 so as to spin the wafer 12 during the SOG process. The thickness and degree of planarization of the SOG coating can be controlled by adjusting the speed of the servo motor 13. During the SOG process, however, the edge of the wafer 12 will also be covered by the SOG, thus forming a spread of fine SOG particles. Conventionally, these fine SOG particles can be removed by a so-called edge bead rinse (EBR) device. As shown in FIG. 1, the EBR device includes a nozzle 14 for jetting a stream of solvent on a margin of about 1 to 2 mm in width on the edge of the wafer 12, by which the fine SOG particles thereon can be washed away.
One major drawback of the foregoing EBR process, however, is that if the solvent is jetted on the edge of the wafer 12 during a high jetting speed or in a great amount, the solvent could be oversprayed elsewhere on the wafer 12, which would substantially affect the planarization of the coating of the SOG layer. In addition, due to the centrifugal force from the spinning of the wafer 12, the solvent jetted on the edge of the wafer 12 will be partly thrown tangentially away from the wafer 12 bumping into and bouncing back from the inner wall 15 of the bowl-shaped area inside 10 onto the wafer 12. This also would affect the planarization of the coating of the SOG layer. Without effective planarization, the final product of the IC chip could lack a quality yield. There exists, therefore, a need for an improved EBR device which is capable of preventing the solvent that is jetted on the edge of the wafer from being sprayed elsewhere on the wafer.